I am about to buy a 100/2.8 USM Macro lens for my Canon 5D. A friend has the 50/2.5 Macro lens and a life size converter for it. I have not seen a life size converter for the 100/2.8. Is there such a thing or is it a moot point with the 100/2.8

Robert

The 100 2.8 Macro is life size, and an great lens.
I've used the shorter extension tube and found the image quality suffered a bit.

The 100 Macro is much faster to focus then the 50 Macro.

I've owned both, and much prefered the 100. David covered the points well, but I'll add this: For me the working distance at closest focus is a lot more comfortable- about half an arm's length. You have to get so close with the 50 that often your shadow, or even the shadow of the lens, can interfere with lighting on small subjects.